Conventionally, there is known a rotary ultrasonic testing apparatus whereby testing is performed while an ultrasonic probe is rotated along the circumferential direction of a test material having a tubular or bar shape.
As shown in FIG. 1, a typical rotary ultrasonic testing apparatus includes: an ultrasonic probe 1 for transmitting/receiving ultrasonic wave to/from a test material S; a probe holder 2 which, with the ultrasonic probe 1 attached thereto, is adapted to rotate in the circumferential direction of the test material S; an ultrasonic flaw detector 3 for controlling the transmitting/receiving of ultrasonic wave to/from the ultrasonic probe 1 and testing the test material S based on an echo received at the ultrasonic probe 1; and a signal transmission section 4 for transmitting a signal between the ultrasonic probe 1 and the ultrasonic flaw detector 3.
In the rotary ultrasonic testing apparatus having the above described configuration, by moving the test material S straight in the longitudinal axial direction and rotating the probe holder 2, and therefore the ultrasonic probe 1 (at around 50 to 2000 rpm), the trajectory of the ultrasonic probe 1 will become a spiral-shape on the surface of the test material S, thereby allowing a rapid testing throughout the entire cross section of the test material S.
Here, known methods for transmitting a signal in a frequency range (1 to 10 MHz) typically used for ultrasonic testing in the signal transmission section 4 include methods of using (1) a slip ring, (2) a capacitive coupling, and (3) a rotary transformer. These methods will now be described one by one.
(1) Method of Using a Slip Ring (See, for Example, Patent Literature 1)
In this method, as shown in FIG. 2, a stationary-side electrode 41A and a rotating-side electrode 42A are provided in the signal transmission section 4 (see FIG. 1). A brush 43 is provided between the stationary-side electrode 41A and the rotating-side electrode 42A. The stationary-side electrode 41A is electrically connected with the ultrasonic flaw detector 3 (see FIG. 1). On the other hand, the rotating-side electrode 42A is electrically connected with the ultrasonic probe 1 (see FIG. 1) and adapted to rotate integrally with the ultrasonic probe 1 (the probe holder 2) (see FIG. 1).
Accordingly, the stationary-side electrode 41A and the rotating-side electrode 42A are brought into contact via the brush 43 to cause signal transmission between the ultrasonic probe 1 and the ultrasonic flaw detector 3.
Since this method is based on a contact scheme, a problem is that it is not suitable for high-speed rotation and its maintainability is very low.
(2) Method of Using a Capacitive Coupling (See, for Example, Patent Literature 2)
In this method, as shown in FIG. 3, a stationary-side electrode 41B and a rotating-side electrode 42B are provided in the signal transmission section 4 (see FIG. 1). A dielectric substance 44 such as air and water is retained between the stationary-side electrode 41B and the rotating-side electrode 42B. The stationary-side electrode 41B is electrically connected with the ultrasonic flaw detector 3 (see FIG. 1). On the other hand, the rotating-side electrode 42B is electrically connected with the ultrasonic probe 1 and adapted to rotate integrally with the ultrasonic probe 1 (the probe holder 2) (see FIG. 1).
Thus, as described above, signal transmission between the ultrasonic probe 1 and the ultrasonic flaw detector 3 is achieved by the dielectric substance 44 being retained between the stationary-side electrode 41B and the rotating-side electrode 42B, thereby forming a capacitor.
When air is used as the dielectric substance 44, this method has a problem of poor maintainability since the transmission efficiency of the air is small, and therefore the distance between the electrodes needs to be very small (about 0.1 to 0.5 mm).
On the other hand, in the method of using a capacitive coupling, when water is used as the dielectric substance 44, it is necessary to retain water uniformly although the distance between electrodes can be fairly large (about 2 mm).
When multi-channel signal transmission is performed (a plurality of ultrasonic probes 1 are provided), in order to retain water W uniformly, it is necessary to arrange a plurality of stationary-side electrodes 41C and the rotating-side electrodes 42C in the longitudinal direction of the test material S, as shown in FIG. 4. For this reason, the length of the signal transmission section 4 increases in the longitudinal direction of the test material S, thus leading to an upsizing of the ultrasonic testing apparatus. Moreover, if the diameter of the test material S increases, the diameter of the signal transmission section 4 also increases, making it more difficult to retain water W.
(3) Method of Using a Rotary Transformer (See, for Example, Patent Literature 3)
In this method, as shown in FIG. 5, a stationary-side coil 45 and a rotating-side coil 46 are provided in the signal transmission section 4 (see FIG. 1). The stationary-side coil 45 is electrically connected with the ultrasonic flaw detector 3 (see FIG. 1). On the other hand, the rotating-side coil 46 is electrically connected with the ultrasonic probe 1, and adapted to rotate integrally with the ultrasonic probe 1 (the probe holder 2) (see FIG. 1).
Thus, signal transmission between the ultrasonic probe 1 and the ultrasonic flaw detector 3 is performed through electromagnetic induction generated between the stationary-side coil 45 and the rotating-side coil 46.
This method is advantageous in that air A may be provided between the coils, and moreover the distance between the coils can be large unlike the above described method of using a capacitive coupling.
However, since the rotary transformer which is formerly proposed for the signal transmission section 4 of the rotary ultrasonic testing apparatus takes on a form in which a plurality of stationary-side coils 45 and a plurality of rotating-side coils 46 are arranged in the longitudinal direction of the test material S in the same manner as with the above described stationary-side electrode 41C and the rotating-side electrode 42C when performing multi-channel signal transmission (a plurality of ultrasonic probes 1 are provided), a problem is that the length of the signal transmission section 4 increases in the longitudinal direction of the test material S, thereby leading to an upsizing of the ultrasonic testing apparatus.
Here, as the rotary transformer, there is known a plate-type rotary transformer, including a plate-shaped stator having a coil arranged on one surface thereof, and a plate-shaped rotator having a coil arranged on one surface thereof, in which the respective coil-arranged surfaces of the stator and the rotator are disposed to face with each other, so that a signal is transmitted between the coils facing with each other (see, for example, Patent Literatures 4 and 5).
It is expected that applying the above described plate-type rotary transformer as that for the signal transmission section of the rotary ultrasonic testing apparatus will suppress upsizing of the ultrasonic testing apparatus even when multi-channel signal transmission is performed. That is, it is expected that adopting a configuration in which a plurality of coils are arranged for each of the stator and rotator constituting the plate-type rotary transformer, and the test material is inserted through a central hole of the plate-type rotary transformer will reduce the length of the signal transmission section in the longitudinal direction of the test material, thereby allowing to suppress upsizing of the ultrasonic testing apparatus.